Neural Phenotypes in Bipolar & Depressive Disorders: The Center application proposes to test two, related hypotheses. The primary hypothesis is that two of the most serious mood disorders, bipolar disorder (BPD) land major depressive disorder (MDD) have distinct neural phenotypes or biological signatures in the brain as identified by a set of non-overlapping alterations in the pattern of expression of individual genes or functionally related ensembles of genes. The secondary hypothesis is that a smaller set of genes will show alterations in common in these diseases and may represent mechanisms related to common vulnerability to mood disorders or a common impact to those disorders on the brain. Project 1 contributes to the investigation of these hypotheses with three Aims. Aim I: Confirm, characterize and investigate selected genes and pathways which are strongly implicated in BPD and MDD contrasted with controls and schizophrenics. Methods to be employed to achieve the goals of Aim 1 include qRT -PCR, in situ hybridization studies, Western blot protein function studies and SAGE (serial analyses of gene expression). Two findings have been selected for in-depth characterization and study (The FGF system which was significantly dysregulated in MDD and mitochondrial dysfunction which is strongly implicated in both MDD and BPD). Aim l will extend the microarray studies to additional limbic and non-limbic structures in BPD and MDD contrasted with controls. There is scientific consensus that the limbic system is a key circuit in the pathophysiology of BPD and MDD. This will represent the first study evaluating gene expression in 3 limbic structures in controls and mood disorder patients. Aim 3 will test the ability to blindly predict and discriminate BPD from MDD and SZ. Based on the neural phenotypes defined by the initial cohorts, predict and discriminate BPD, MDD from SZ in a new cohort of 15 BPD, 15 MDD and 15 controls. Information derived from the following sets of data will be utilized in the predictive analyses: Unique non- overlapping genes for BPD and MDD; the same genes significantly different in opposite directions in BPD and MDD; genes shared in common between BPD and MDD; GO and KEGG pathway and function analyses of BPD and MDD. The identification of validated and replicated genes and pathways that can predict MDD as distinct from BPD will constitute a major contribution to investigating the etiology of these disorders and toward! identifying novel targets for their treatment or prevention. These investigations have many conceptual and technical links with other Center projects and depend on the support provided by all of the proposed Cores.